1. Field of the Invention
The present invention relates to a nitride semiconductor light-emitting device.
2. Description of the Related Art
Generally, a light-emitting device is a kind of a semiconductor device used for converting electricity into an infrared or light using a characteristic of a compound semiconductor to transmit and receive a signal. The light-emitting device is widely used for home appliances, remote controllers, display boards, display apparatuses, and a variety of automation apparatuses.
In operation, when a forward voltage is applied to a semiconductor formed of a predetermined element, an electron and a hole recombine at a positive-negative junction portion. At this point, an energy level falls down due to recombination of an electron-hole pair, so that light is emitted.
Also, a light-emitting device is generally manufactured in a very small size of 0.23 mm2, and provided in a structure in which the light-emitting device is mounted in a printed circuit board (PCB) using an epoxy mold and a lead frame. A light-emitting device most widely used currently is a 5-mm plastic package but is not limited thereto and a new type of package is under development depending on a predetermined application. A wavelength of light emitted from a light-emitting device is determined by a combination of elements constituting a semiconductor chip.
A related art nitride light-emitting device will be described with reference to the accompanying drawings.
FIG. 1 is a cross-sectional view of a related art light-emitting device. A light-emitting device, which will be described below, is a light-emitting device using a nitride semiconductor, specifically, a gallium nitride.
Referring to FIG. 1, the related art light-emitting device includes a buffer layer 20, un-doped GaN layer 30, an n-type first conduction-type cladding layer 40, an active layer 60, a p-type second conduction-type cladding layer 70, an n-type electrode 50, and a p-type electrode 80 sequentially formed on a substrate 10 exemplified as a sapphire substrate.
A method for manufacturing the related art light-emitting device is sequentially described in detail.
First, the buffer layer 20 is formed on the substrate 10 in order to grow high quality nitride, so that a planarization of the substrate 10 is increased. For example, melt-back etching caused by a chemical reaction of the substrate 10 is prevented.
Also, the un-doped GaN layer 30 grows the n-type first conduction-type cladding layer 40 thereon, as a base layer for various semiconductor layers to be formed on the buffer layer 20.
Subsequently, the active layer 60 and the p-type second conduction-type cladding layer 70 are grown on the n-type first conduction-type cladding layer 40.
Here, the active layer 60 having a multiple quantum well (MQW) structure is a layer where holes flowing through the p-type electrode 80 and electrons flowing through the n-type electrode 50 recombine, thereby emitting light.
With this state, the n-type electrode 50 is electrically connected on an upper portion of the n-type first conduction-type cladding layer 40, which is a portion on which the p-type second conduction-type cladding layer 70 and the active layer 60 are not grown, more strictly, a portion exposed by growing at least the p-type second conduction-type cladding layer 70 and the active layer 60 and then removing a portion of the grown layers 70 and 60. Also, the p-type electrode 80 is electrically connected on the p-type second conduction-type cladding layer 70.
When a voltage is applied to the light-emitting device through the n-type electrode 50 and the p-type electrode 80, electrons are injected to the active layer 60 from the n-type first conduction-type cladding layer 40, and holes are injected to the active layer 60 from the p-type second conduction-type cladding layer 70. At this point, the electrons and holes injected into the active layer 60 recombine to generate light.
As described above, a sapphire substrate of substrates of various materials are generally used in the nitride light-emitting device. Although a sapphire substrate has an insulation characteristic and shows a high lattice mismatch of about 15-17% with respect to a GaN-based semiconductor material, the sapphire substrate is thermally stable and thus has little thermal damage at a range of about 1,000-1,200° C. during an epitaxial layer growth that uses metal oxide chemical vapor deposition (MOCVD). Also, the sapphire substrate is known as a high quality material of low defect concentration.
However, since the sapphire substrate in an insulator, a rear side contact is impossible during a device fabrication, so that there are lots of difficulties during a manufacturing process. Accordingly, it is general to perform a contact by performing dry-etching on a portion of a grown epitaxial layer, which is known in detail to the related art.
When dry-etching is performed on a related art nitride light-emitting device to etch a portion of an already grown epitaxial layer, a light-emitting area is reduced. When a chip size is reduced, an interval between a p-type electrode and an n-type electrode narrows, there is a high possibility that a short-circuit between the electrodes occurs. Also, there is a problem that a grown epitaxial layer is damaged during drying etching, and generates a defect, resulting in reduction of a light-emission efficiency. Consequently, these problems reduce brightness and reliability of a light-emitting device.